Custom Molded Rubber
Custom Molded RubberCustom Molded RubberColumbia Engineered Rubber - HomeMolded Rubber ProductsColumbia Engineered Rubber - ContactsColumbia Engineered Rubber - About UsRubber Component Design Reference
Custom Molded Rubber
O-rings and Seals
Rubber Bellows, Rubber Boots and Convoluted Boots
Vibration Isolators and Mounts
Formed Rubber Hose
Materials and Elastomers
Back
Custom Molded Rubber
Compression Molding
 
Transfer Molding
 
Injection Molding
Compression Molding
           
Compression molds are the least complex of thermal set molding and can vary in size, shape and complexity, as well as, the number of cavities it contains. The molding process begins with a piece of uncured rubber perform which is shaped to the approximate size and shape of the desired part, and is placed directly in the mold cavity prior to mold closure. The rubber is then compressed between the top and bottom plates and heated. Causing the compound to flow, filling the cavities and spilling out into overflow grooves. The uncured rubber must weigh more than the finished part in order to rid of all the air.
This type of molding process offers lower tooling and set-up costs, short molding cycles, lower unit cost, little to no flash and reduced waste
Back          
           
Transfer Molding
           
The transfer molding process beginning with the uncured rubber placed in a transfer plate located above the cavity area, rather than being placed directly in the cavity as in compression molding applications. heat is then applied to the rubber and transferred from the transfer plat, being pushed through a gate by a piston, into the cavity where the rubber is then vulcanized using heat and pressure.
Back          
           
Injection Molding
 
The injection molding process is the most automated application. The rubber material is heated to a easily flowing state and then injected under pressure from the heating chamber to the mold. This application is most applicable for high volume production.
Back          
Producing a successful product begins with a proper design. Many of Columbia's customers will partner with us for our expertise in tool design. A well designed tool will not only maximize the end products performance but also minimize the cost of production. At Columbia Engineered Rubber Inc. our molding capabilities include the three major molding process: transfer molding, compression molding and injection molding. We will select the right molding application for your product based on several key factors including, but not limiting to; the size, shape and number of parts you desire. Here at Columbia we will not only find the correct molding application but the most cost efficient one as well. The following is a brief summary of the different molding applications Columbia offers
Molding Processes
Mold Design
Molds can be designed at varying degrees of precision, however, not at the same cost. With any mold their must be some tolerance and therefore each cavity will have some variance from the others. The accuracy of the mold register must also be considered. This is the matching of the various plates of the mold that form the mold cavity. Products requiring a high degree of precision, in both the dimensions and the registrar require more precise design work and machining and therefore increasing the overall price.
 
Insert
Most inserts actually have their own standard tolerances, but when used in rubber materials other factors must be considered. Such as: fit in the mold, cavities, location of the insert, hole spacing to match with mold pins ect.
Factors Affecting Tolerances
 
Shrinkage
Defined as the difference between the corresponding linear dimensions and the molded part, is applicable to all rubber products. All rubber material experience some amount of shrinkage and it is up to the mold designer and the compounder to determine the amount of shrinkage the material will exhibit and incorporate this allowance into the mold cavity size. Shrinkage itself is a variable and is affected by such factors as material specification, cure time, temperature, pressure etc. The skill of the rubber manufacture is to limit these variables however, they cannot be eliminated entirely.
 
Environments Storage Conditions
Humidity: Some rubber material absorb moister, therefore the dimensions are affected be the amount of moister the product absorbs. This can be prevented by storing the product in a controlled environment or having additional tolerances. Temperature: Compared to other materials the coefficient of expansion in rubber is high. To have an agreement in measurement the temperature at which the product is to be measured at and the time required to stabilize the part at that temperature
 
Distortion
Seeing that rubber is a flexible material, its shape can be affected from such thins as removal from the mold, shipping and temperature changes. A good way to help prevent such distortion is to let the finished product sit at room temperature for 24 hours before shipping, other actions can be discussed with the rubber manufacture.
 
Trim & Finish
The objective of trimming and finishing a product is to remove excess material, such as flash, which is not part of the finished product. For a more precise trim mechanical finishing may control the finished dimensions.
 
Line Call-Outs
SI -
The letter M is used to indicate that the classification is based on SI units. Any other prefix refers to an earlier classification system based on inch-pound units.
 
Type and Class -
Type refers to heat resistance and Class refers to oil resistance. Type (indicated by the letter B in the example) is based on tensile strength of not more ±30 %, elongation no more than -50 %, hardness no more than ±15 points, after being heat aged for 70 h. The temperature at which the test must be conducted is represented by the prefix under type and its corresponding value.Class is the resistance of a material in an ASTM oil No.3 after 70-h of heat aged testing designated from the previous type.
 
Hardness -
The letter designations are always followed by a three digit number that specify the hardness and tensile strength. The first digit indicates the durometer hardness, the nest two digits indicate the tensile strength
 
Grade Numbers and Suffix Requirements -
Grade Numbers are used when the basic requirements are not sufficient enough for a particular application. A Grade number of one indicates that only the basic requirements are necessary any other grade is used to express deviations or additional requirements. These are found in the example below the suffix requirements header. Suffix Letters - meanings can be found in the corresponding ASTM tables. Suffix Numbers - Each suffix letter should be followed by two suffix numbers, the first digit represents the test method and the second represents the heat at which tested at.
 
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org.
This type of classification tells the engineer the properties of a particular rubber material that is intended for, but not limited to, automotive applications. This classification is designed so rubber products can be arranged into characteristic material designations. The purpose of this is to provide guidance in the selection of a particular rubber material, and specifying the materials by using a simple method called Line Call-Outs.All Classifications and descriptions of the corresponding prefix or numbers can be referenced a specific ASTM D2000 table that can be found at astm.org.
   
Product Example
ASTM D 2000 M2BC 507 A14EO34 		 
Rubber Design
 
Type and Class Polymer Usage - This table is a reference for the Classification System D 2000-SAE J200 and is not part of the system itself
Rubber Design
ASTM D2000 Standard Classification System for Rubber Products used in Automotive Applications
ASTM D2000 Classification Molding Applications
ASTM D2000 Material Designation 1. Compression Molding
Factors Affecting Tolerances 2. Transfer Molding
  3. Injection Molding
Rubber Classification and Design » Molding Processes