Amelia Hu 's Blog

What are the reasons for “fiberglass exposed phenomenon ” and how to solve it ?—By SFMA GROUP

Amelia Hu — Wed, 27 May 2015 02:04:50 +0000

What is “fiberglass exposed phenomena ”:

White fiberglass exposed on the exterior during plastic filling flow process , after condensation it will left radial white marks on the plastic surface . It will be severer if the plastic is black.

There are several reasons to be listed below:

1.During the plastic melt flow process, because the glass fiber and resin flowability and density are different, the two have a tendency to be separated, lower density (fiberglass )will float to the surface, higher density(resin) will sink inside, thus forming the “ fiberglass exposed phenomenon ”.

2.The plastic can cause localized differences in viscosity by frictional shear forces of screw, nozzles, runner and gate in the flow process, at the same time it will damage the surface of the interfacial layer of fiberglass , The smaller of melt viscosity , the more serious damage will be caused to the interface layer , adhesion between the glass fiber and resin also become smaller .When the adhesive force is small to a certain extent,it will get rid of the shackles of fiberglass resin matrix, gradually accumulated on the surface and exposed.

3.Furthermore, when the plastic melt into the cavity, it will has a “fountain” effect, namely the fiberglass will flow into contact with the internal cavity surface, due to the lower mold surface temperature, light weight , easily condensated fiberglass are quickly frozen, if not be fully surrounded by the melt in a timely manner , it will be exposed .

So How to solve it ?

High melt temperature, high mold temperature, high injection pressure, high speed, low injection speed are quite favorable to improve the “fiberglass exposed ” if you are not considering additives.

Since the basic principle of gating system design is that the gate section should be large,the flow process should be straight and short. Stubby sprue , runner , gate are better options. Film gate ,Fan gate , Ring gate and multi gate could achieve purpose such as melt flow orderless , fiberglass diffused, orientation reduced. Also good venting system can discharge the volatile generated by the fiberglass surface treatment agent , to avoid defects such as burns ,short shots ,poor welding and etc.

Another thing to note is that the “fiberglass exposed ”normally happen at thick wall area , cause the melt ’s flow velocity gradient is larger , the center speed of the flow is higher , While the melt’s speed close to the cavity is lower , which increase the fiberglass exposed tendency .

Therefore, It should be of uniform thickness throughout plastic parts .Sharp corners, notches are not recommended if you want to ensure melt flow smoothly.Since fiberglass reinforced plastic melt index is lower than non-reinforced plastics by 30%-70% , the fluidity is not that good ,so the barrel temperature should be higher than usual by 10 ~ 30 ℃.

Increase barrel temperature can not only reduce the melt viscosity, improve fluidity, avoid short filling and poor welding,but also could help to increase the fiberglass dispersion and reduce orientation, get a lower roughness surface . But ,it’s not the higher the better , higher temperature will increase the polymers’ oxidation and degradation tendency, a slight color change will occur , worse , being blackened .

When setting the barrel temperature, feed zone temperature should be slightly higher than the regulatory requirements, slightly lower than the compression section , which can take advantage of its warm-up effect, reduce the shear forcesof screw on fiberglass, decrease localized differences in viscosity and the damage surface of the fiberglass’ interfacial layer, to ensure the bond strength between fiberglass and resin .

As we mentioned before ,the temperature difference between the mold and the melt should not be too large, so higher mold temperature could increase the melt filling performance, weld line strength, improve product surface finish, reducing orientation and deformation is also a benefit.

But higher die temperature needs longer cooling time, molding cycle is lengthened, productivity is lower,mold shrinkageincreased as well .

Other options to solve the “fiberglass exposed phenomena ”

You could add compatibility, dispersant and lubricant additives in the molding material, comprising a silane coupling agent,maleic anhydride-grafted compatibility agent, silicone powder,fatty acids, lubricants and some domestic or imported Anti-fiberglass exposed agent etc.

These additives are to improve the interface compatibility between fiberglass and resin , enhance the uniformity of dispersed and continuous phases, heighten interfacial adhesion strength and reduce separation between fiberglass and resin .

But for liquid silane coupling agent, it is difficult to disperse after joining , when the plastic tends to agglomerated it will cause the nonuniform material feeding ,fiberglass nonuniform distributed , which lead to nonuniform mechanical properties of products .

If you have any question about thermoplastic resin + Fiberglass molding issue , please feel free to talk to one of our expert at : sales@sfmagroup.com .

Low Pressure Injection Moulding enables production of large parts

Amelia Hu — Tue, 09 Aug 2011 01:23:24 +0000

For more information , please watch our company’s video at :

Cordially

Amelia
B2B Marketing and Social Networking
CN Mould & Plastic Limited (Video: http://www.youtube.com/watch?v=u2lgkSbNNkg )
Add: CN Hi-Tech industry park, No.227, Xiangshan Rd., Luotian 3rd industry zone, Songgang, Baoan, Shenzhen, 518105, China.
Tel: 86-755-86060383, 86061383, 86060363 Ext:828
Fax: 86-755-86060393
Skype: niya2000007
MSN : cntsales@live.cn
Email: sales@cnmouldplas.com
Website: http://www.cnmouldplas.com

Injection Molding Cycle Time

Amelia Hu — Mon, 25 Apr 2011 03:23:44 +0000

Cycle Time,

is the time required to close a mold, inject the material, cool the material, open the mold, eject the part, and, in the case of inserts, reset the mold.

Cycle times can be made faster by having well-designed parts with walls that maintain a uniform thickness and which are no thicker than necessary. Thick-walled parts take longer to cool due to the extra material and slow down cycle times.

On a per part basis, cycle times can be greatly improved by adding additional cavities to the molds. By using multi-cavity molds one cycle can produce several parts instead of just one in the same amount of time.

Cordially

Amelia
B2B Marketing and Social Networking
CN Mould & Plastic Limited (Video: http://www.youtube.com/watch?v=u2lgkSbNNkg )
Add: CN Hi-Tech industry park, No.227, Xiangshan Rd., Luotian 3rd industry zone, Songgang, Baoan, Shenzhen, 518105, China.
Tel: 86-755-86060383, 86061383, 86060363 Ext:828
Fax: 86-755-86060393
Skype: niya2000007
MSN : cntsales@live.cn
HP: 86 135 6078 9420
Email: sales@cnmouldplas.com
Website: www.cnmouldplas.com

Injection Molded Parts Design–by Elito

Amelia Hu — Mon, 04 Apr 2011 08:59:07 +0000

Injection molded parts are made of thermoplastics, a polymer that turns into liquid when heated then turns back to solid when cooled.

Carefull thoughts on the following elements shall be considered for the design of plastic injection molded part.

Wall Thickness

As much as possible use a uniform wall thickness. If you must change the wall thickness, change it gradually to avoid warping.

If the strength is not compromised, design the part with minimal wall thickness to allow faster cooling time and cycle time.

Draft angles

Draft angle is necessary for easy removal of molded part from the mold. Draft angle should be applied in the direction of draw from the cavity and core.

Parts with textured surface require greater draft angle in order to avoid scratches on the textured surface as the part is being removed from the mold. 1 to 3 degrees normally applies to moderately matte or sand-blasted surfaces and 3 to 5 degrees for roucher surface.

But for smaller precision molded parts, it is sometime unnecessary to include draft angles as long as the cavity and core are highly polished.

Corner Radius

Apply radius on corners as much as possible. A proper radius size is not less than the wall thickness of the part.

Radius reduces the stress on the corner thus reducing the warpage compared to corners without radius.

Rib

Apply rib instead of using thicker wall thickness. Uneven cooling of thick wall will lead to uneven shrinkage inside and outside the wall. This could cause warpage and sinkmark due to internal stress. Applying rib will help improve the rigidity and geometric integrity of the molded part. It also improves the cooling time.

Mold Standards

Amelia Hu — Mon, 21 Mar 2011 07:32:02 +0000

Molders and Moldmakers can build a mold in a wide variety of ways – ranging from the quick & economical prototype mold to the super high quality, long lasting production mold. The problem is in making sure that when a mold is quoted everyone involved is “on the same page”.Detailed Mold designs featuring a full Bill of Materials, Assembly drawings, and Detail drawings.

A-Series DME Standard Mold Bases, #2 Steel (28-30R/C).

Cavity & Core Machined in P-20 Steel Inserts (30-32 R/C) [However, about 50% of the molds we build utilize hardened H-13, S-7, or 420SS (48-58 R/C). We try to recommend core & cavity materials based upon what we know about the project – part material, production amounts, life of the program, cycle requirements, expected maintenance, etc.]

SPI #3 Cavity Finish.

Water/Cooling lines in Cores and Cavities (and in sub-inserts & slide bodies if feasible) with connectors.

Guided Ejection system with Spring Loaded Return & Tapped Knock-out holes.

Lifters typically have a Core and a separate lifting rods, Lifter guide bushings, and replaceable gib/couplings.

Tunnel (sub) gate if possible (Edge/Chisel gate if Tunnel gate is not feasible).

Hot Runner Systems are typically built in-house with Standard DME components OR purchased from a recomended hot runner supplier.

Mold is stamped with Customer Name, Part Name, Part Number, Approximate Weight, and Manufacture Date. Inserts and Details are stamped with Material type and Detail Number.

Also, we try to recommend Parting Line Locks, Switches, Early Ejector Return Systems, Accelerated Ejectors, as well as other components and peripherals when we believe they are necessary.

SPI: MOLD CLASSIFICATIONS

Amelia Hu — Mon, 14 Mar 2011 08:07:37 +0000

INTRODUCTION

The following classifications are guidelines to be used in obtaining quotations and placing orders for uniform types of molds. It is our desire through these classifications to help eliminate confusion in the mold quote system and increase customer satisfaction. It is strongly recommended that mold drawings be obtained before construction is started on any injection mold. Even though parts may seem simple enough not to warrant a mold design, a drawing showing sizes and steel types will pay for itself in event of mold damage. These classifications are for mold specifications only and in no way guarantee workmanship.

It is very important that purchasers deal with vendors whose workmanship standards and reliability are well proven.

Mold life, because of variations in part design and mold conditions, cannot be guaranteed. This guide will attempt to give approximate cycles for each type of mold excluding wear caused by material abrasion, poor mold maintenance and improper molding technique. Maintenance is not the responsibility of the moldmaker. Normal maintenance such as replacement of broken springs, broken ejector pins, worn rings, or the rework of nicks and scratches should be borne by the molder. Mold rework costs should be closely considered when deciding which classification of mold is required. This document does not constitute a warranty or guarantee by the Society of the Plastics Industry, Inc., or its members for the classifications or specifications set forth herein.

CLASSIFICATION OF INJECTION MOLDS UP TO 400 TONS

The following contains a brief synopsis of the various mold classifications and the detailed descriptions of each mold class. Again, it is our recommendation that a MOLD DATA SHEET (an example of which is in the back of the SPI manual) be included with each request for quotation.

GENERAL SPECIFICATIONS

1. Customer to approve mold design prior to start of construction.

2. All molds, with the exception of prototype, to have adequate channels for temperature control.

3. Wherever feasible, all details should be marked with steel type and Rockwell hardness approximately .005 deep.

4. Customer name, part number, and mold number should be steel stamped on mold.

5. All molds should have eyebolt holes on the top side. There should be one above and one below the parting line to facilitate mold removal, if required, in halves.

CLASS 101 MOLD

Cycles: One million or more

Description: Built for extremely high production. This is the highest priced mold and is made with only the highest quality materials.

Detailed mold design required.

Mold base to be minimum hardness of 28 R/C.

Molding surfaces (cavities and cores) must be hardened to a minimum of 48 R/C range. All other details, such as sub-inserts, slides, heel blocks, gibs, wedge blocks, lifters, etc. should also be of hardened tool steels.

Ejection should be guided.

Slides must have wear plates.

Temperature control provisions to be in cavities, cores and slide cores wherever possible.

Over the life of a mold, corrosion in the cooling channels decreases cooling efficiency thus degrading part quality and increasing cycle time. It is therefore recommended that plates or inserts containing cooling channels be of a corrosive resistant material or treated to prevent corrosion.

Parting line locks are required on all molds.

CLASS 102 MOLD

Cycles: Not exceeding one million

Description: Medium to high production mold, good for abrasive materials and/or parts requiring close tolerances. This is a high quality, fairly high priced mold.

Detailed mold design required.

Mold base to be minimum hardness of 28 R/C.

Molding surfaces should be hardened to a 48 R/C range. All other functional details should be made and heat treated.

Temperature control provisions to be directly in the cavities, cores, and slide cores wherever possible.

Parting line locks are recommended for all molds.

The following items may or may not be required depending on the ultimate production quantities anticipated. It is recommended that those items desired be made a firm requirement for quoting purposes:

a. Guided Ejection

b. Slide Wear Plates

c. Corrosive Resistant Temperature Control Channels

d. Plated Cavities

CLASS 103 MOLD

*Cycles: Under 500,000

Description: Medium production mold. This is a very popular mold for low to medium production needs. Most common price range.

Detailed mold design recommended.

Mold base must be minimum hardness of 8 R/C.

Cavity and cores must be 28 R/C or higher.

All other extras are optional.

CLASS 104 MOLD

*Cycles: Under 100,000

Description: Low production mold. Used only for limited production preferably with non-abrasive materials. Low to moderate price range.

Mold design recommended.

Mold base can be of mild steel or aluminum.

Cavities can be of aluminum, mild steel or any other agreed upon metal.

CLASS 105 MOLD

Cycles: Not exceeding 500

Description: Prototype only. This mold will be constructed in the least expensive manner possible to produce a very limited quantity of prototype parts.

May be constructed from cast metal or epoxy or any other material offering sufficient strength to produce minimum prototype pieces.

Mold Design Checklist

Amelia Hu — Mon, 07 Mar 2011 00:52:22 +0000

The following is a good checklist for reviewing Mold Drawings

Preliminary Drawing Checklist Items:

General layout

“A” side plan

“B” side plan

Front Section

Side Section

Title block is completely filled out on all drawings

Abbreviated BOM with ordering information for the Mold Base and primary Steels

Cavity Location

Parting line locations (Acceptable to customer)

Ejector Pin Layout (Acceptable to customer)

Waterline Layout

Balanced Runner layout

Gate type, and size specified

Side Action types & locations are shown

Concept of Tool operation

“O” & “R” Dimensions noted

Note “Top of mold” & “Operator Side”

Will the tool fit in the correct press size

Knock out Locations

Support pillar layout

* Typically, approval of the Preliminary designs approves our design concept. Customer approval means that we can proceed with the Final Designs, that we can order the necessary materials, and that we can begin rough machining of material. Sometimes, especially on “rush” jobs, customers approve finish machining based on the preliminary design.

Final Drawing Checklist Items:

All Preliminary Mold Drawings Requirements completed

Full Bill of Materials, Base Information, stamping notes, ejector information, special notes

Detailed views of every non-standard component.

Enough views, sections, iso views exist to adequately show part detail

All details are labeled with the detail number, name, material type, number required, Hardness, and surface finish.

Check All water lines for interference, including clearance for jiffy-plugs

Check Guide Pin length and clearance

Spring loads calculated & checked

Drawings appear to be adequately dimensioned

Critical Dimensions are noted

All “fit” areas are specified for each insert, side action, and core.

All draft is specified for cavity area, core pins, ribs, etc.

Check all side action angles and travel

Check for bad steel conditions (sharp edges, thin sections, too little shutoff, too little angle)

A & B Plan assembly views have been compared

All details from the assembly and plan views have been compared to the detail sheets.

All surface finishes are specified

Drawings are checked to the “Mold Info Sheet”.

* Typically, by approving the Final designs the customer certifies that the drawings are dimensionally accurate, that critical areas have been noted, and that we can proceed with final machining, fit, and finishing.

Injection Molder and Molding Machines

Amelia Hu — Mon, 28 Feb 2011 03:07:17 +0000

Injection molder or injection molding machine is a machine for producing plastic molded parts by molding process. It has 2 main parts, an injection unit and a clamping unit.

An injection molder have 2 methods of fastening the mold -horizontal or vertical. Most injection molder are horizontally oriented because molded parts can easily be removed after ejection by leveraging gravity -the molded parts will just fall down into the container below. Vertical injection molders are used for insert molding applications because inserts are inserted into the core side of the mold before molding.

There are also manual injection molder for hobbyists. It is simple in consruction and does require manual force to inject the resin. An example of such machine is from Galomb, Inc. They make Benchtop injection molder.

Types of injection molding machines

Injection machines are classified mainly by the type of system that drives them: Hydraulic, electric, or hybrid.

Hydraulic injection machines uses ram system for its clamping mechanism. This type of machine is used by majority of molding companies.

Electric injection machines are driven by motors. Unlike the hydraulic machines, which continously pump hydraulics to the cylinder throughout the whole molding cycle, an electric machine only makes use of energy during closing and openning of the clamping unit. It uses toggle system for its clamping mechanism in order to build up tonnage. It is also faster, quieter, and have higher accuracy, but it is also known to be more expensive. The first maker of electric injection machine is Nissei Plastic Industrial Co., LTD.

Cordially

Functions of Mold Base Parts—By Elito

Amelia Hu — Fri, 18 Feb 2011 07:03:44 +0000

Fixed Clamping Plate
Holds The fixed side of the mold to the fixed platen of the injection machine.

Locating Ring
It is used to locate the center of the injection machine so that the sprue bushing and the nozzle are aligned. Commonly fitted into the counterbore in the fixed clamping plate.

Fixed Cavity Plate
Used to hold the fixed cavity block, leader pin/bushing, and sprue bushing.

Movable Cavity Plate
Used to hold the movable cavity block, leader pin/bushing.

Movable Clamping Plate
Holds The movable side of the mold to the movale platen of the injection machine.

Spacer Block
Mounted between the movable clamping plate and the movable cavity plate to give space and allow the ejector plate to move when ejecting the
part.

Ejector Retainer Plate
Holds the ejector pins and the return pins in place.

Ejector Plate
Pushes the ejector pins and return pins at the same time. Mounted to the ejector retainer plate to form the ejector unit.

Support Pillars
Bars placed between the spacer blocks to give additional support to the movable cavity plate.

Sprue Bushing
Has a tapered hole through which the material is forced into the runner. It is butted up against the nozzle of the injection machine.

Return Pins
Same as ejector return pins. Make sure that the ejector unit is back in its original position when the mold closes.

Leader Pins and Bushings
Precisely align the two halves of the mold base (fixed and movable).

Cordially

A Typical Injection Mold Design Guid —-by Elito

Amelia Hu — Sun, 23 Jan 2011 13:05:19 +0000

This checklist can be used as a general reference guide for injection mold design engineers. It is divided into 3 parts of a mold design process.

Part 1 – Requirements to start your mold design:

1, Check the injection machine where the mold is to be mounted. This will help you decide the size and structure of the mold for ease of installation and other factors. Important notes:

Locating ring size (or other positioning method)

Nozzle size

Method of clamping (Auto or manual)

Temperature control system

2, Determine the number of cavities and volume requirements. This will help you decide the material that you are going to use and other mold components that you will choose for cost effective design.

3, Determine the gate location and size.

4, Determine the location where ejector pin marks are prohibited.

Part 2 – Mold base layout:

Place cavities close to the center of the mold to minimize base size and runner length.
Ensure that the molded part remains on the movable half (ejector half) upon opening of PL to facilitate proper ejection.
Waterlines should be placed as evenly as possible to the contours of the cavity.
Use support pillars underneath the cavity pockets.
Use ejector guides for molds with small ejector pins and rectangular ejector pins.
Provide eye-bolt hole for ease of mounting and dismounting.
Install mold opening prevention locks on the operator side.
Establish pry bar groove on the corners of the mold parting line to facilitate ease of mold opening during assembly and maintenance.

By this time you may ask for the mold layout approval from the customer.

Part 3 – Cavity/core details:

Check material shrinkage. Locate portions (corners) for possible significant deflection and deformation.
Maintain uniform wall thickness .
Draft angle should be within dimension tolerance.
Divide core blocks to simplify machining and provide gas vent path.
Gate, small cores, and cores with shut-off fittings are better designed as insertable components for easy modification and repair.
Watch out for possible deformation of core pins.
Position the ejector pins on the ribs and other high strength locations. Ensure ejector balance.
Detailing/part drawing: Include all parameters needed for processing -material, quantity, surface finish/texture, dimensions, tolerances and many more. Do not assume the machinist understands everything.

Any design change and amendments to the mold must be re-approved by the customer or mold owner.

Few extras that could make your mold one step further in terms of quality:

Bevel edges. Whenever possible use machine to bevel the edges.
Minimize scratches on the mold base. Keep the work table clean.

This checklist may be updated regularly so I suggest you “bookmark” if you find it useful.

Cordially

Amelia
B2B Marketing and Social Networking
CN Mould & Plastic Limited (Video: http://www.youtube.com/watch?v=u2lgkSbNNkg )
Add: CN Hi-Tech industry park, No.227, Xiangshan Rd., Luotian 3rd industry zone, Songgang, Baoan, Shenzhen, 518105, China.
Tel: 86-755-86060383, 86061383, 86060363 Ext:828
Fax: 86-755-86060393
Skype: niya2000007
MSN : cntsales@live.cn
HP: 86 135 6078 9420
Email: sales@cnmouldplas.com
Website: www.cnmouldplas.com