### Surface Densification of Reusable Surface

**Insulation Tiles**

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| **Engineering Directorate**                                           |
|                                                                       |
| **Structural Engineering Division**                                   |
|                                                                       |
| **April 2007**                                                        |
|                                                                       |
| ![](media/image1.png)                                                 |
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| National Aeronautics and                                              |
|                                                                       |
| Space Administration                                                  |
|                                                                       |
| **Lyndon B. Johnson Space Center**                                    |
|                                                                       |
| Houston, Texas                                                        |
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**Surface Densification of Reusable Surface**

**Insulation Tiles**

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| **Prepared by:**   |                             |     |           |
+--------------------+-----------------------------+-----+-----------+
|                    | Michael E. Fowler,          |     | Date      |
|                    |                             |     |           |
|                    | Materials and Processes     |     |           |
|                    | Branch/ES4                  |     |           |
+--------------------+-----------------------------+-----+-----------+
|                    |                             |     |           |
+--------------------+-----------------------------+-----+-----------+
|                    | Jeremy Brand                |     | Date      |
|                    |                             |     |           |
|                    | Materials and Processes     |     |           |
|                    | Branch/ES4                  |     |           |
+--------------------+-----------------------------+-----+-----------+

+--------------------+-----------------------------+-----+-----------+
| **Approved by:**   |                             |     |           |
+--------------------+-----------------------------+-----+-----------+
|                    | Brad Files, Branch Chief,   |     | Date      |
|                    |                             |     |           |
|                    | Materials and Processes     |     |           |
|                    | Branch/ES4                  |     |           |
+--------------------+-----------------------------+-----+-----------+

  ----------- --------------------------------------------- ------------------------------------------
  REVISIONS                                                 

  VERSION     CHANGES                                       DATE

  Baseline    Original version                              6/5/98

  A           Reviewed per QMS requirements. Removed        [2/5]{.underline}2/5/02[/02]{.underline}
              reference to NDE (not applicable) in 3.1.     
              Corrected reference to paragraphs 7.1 and 7.2 
              (was 8.1 and 8.2) in 3.1. Corrected reference 
              to SOP-007.1 (was EM-007.1).                  

  B           Clarified Level 2 definition. Updated         
              material specification references. Added      
              BRI-18.                                       

                                                            

                                                            
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**1.0 [SCOPE]{.underline}**

This PRC establishes the requirements for densifying the IML surfaces of
existing Reusable Surface Insulation (RSI) tiles before the Strain
Isolator Pad (SIP) is bonded.

# **2.0 APPLICABILITY**

This specification shall be applicable whenever RSI densification is
invoked per Section 3.0, "Usage".

**3.0 [USAGE]{.underline}**

This section gives the requirements for the proper use of this process
specification. In accordance with the drawing and part definition
requirements of JSC 8500, "Engineering Drawing System Requirements",
this standard manufacturing process shall be invoked by providing a
process note in the applicable drawing or CAD model as exemplified in
Figure 1.

Figure 1. Example of a process note for

densifying RSI tile.

**3.1 LEVELS**

The \"Level\" designator governs the extent to which quality assurance
provisions are applied and shall be specified in the process note on the
basis of the following definitions:

a\. [Level 1]{.underline} --- Level 1 processes shall include the
practice of the quality assurance provisions as required by Section 7.1.

b\. [Level 2]{.underline} --- Level 2 processes shall include the
practice of the quality assurance provisions as required by Section 7.2.

**4.0 [REFERENCES]{.underline}**

The following references were used to develop this process
specification:

SOP-007.1 Preparation and Revision of Process Specifications

JSC 8500 *Engineering Drawing System Requirements*

MA0609-303 Surface Densification of Reusable Surface Insulation Tiles

**5.0 MATERIAL REQUIREMENTS**

**5.1 DENSIFYING MATERIAL**

In order to make approximately one gallon of densification slurry,
combine 1265 grams of MB0115-036 fused silica powder with a quantity of
MB0115-011 colloidal silica as described by the empirical equation
below:

= density of colloidal silica (1.160 to 1.201 g/cm^3^)

The fused silica/colloidal silica slurry mixture shall be turned on a
roller mill for one hour minimum prior to density evaluation. The
evaluation shall be completed within 30 minutes after removal from the
roller. The density of the slurry mixture as determined using weight and
volume measurements shall be 1.37 ± 0.01 g/cm^3^. If the mixture density
falls outside the required range, the density may be adjusted by the
addition of colloidal silica when the density is high or by the addition
of fused silica powder when the density is low. When the proper density
is achieved, add 0.12 percent by weight of MB0115-048 silicon
hexaboride. Roll the mixture on a roller mill until the boron silicide
is uniformly dispersed in the densification slurry.

**6.0 PROCESS REQUIREMENTS**

**6.1 WATERPROOF TEST**

Determine if tile has been waterproofed prior to densification.

**6.2 HEAT CLEANING**

Tiles that absorb water shall be heat cleaned at the temperature of
1275°F ± 175°F for a minimum of 10 minutes prior to densification. Tiles
that do not absorb water do not require a heat cleaning.

**6.3 SURFACE PREPARATION**

**6.3.1 SURFACE**

Area to be densified shall be a machined RSI surface. When previously
densified, a minimum of 0.040 inch shall be removed prior to a second
densification.

**6.3.2 PRE-COAT**

A densification pre-coat consisting of isopropyl alcohol shall be
applied to tiles waterproofed prior to densification. Tiles that have
not been waterproofed shall utilize a densification pre-coat consisting
of 50% Colloidal silica and 50% deionized water applied at 2.0 ± 0.1
g/in^2^.

**6.4 DENSIFICATION**

Apply material prepared in 5.1 to the IML surface and any holes to be
densified in successive coats to attain weight gain of 5.5.1. Remove
excess material so that no buildup is left on the tile surface after
drying.

**6.4.1 WEIGHT GAIN**

Densification shall result in a weight gain of solids (water and alcohol
excluded) within the limits presented in Table I.

Table I. Surface Identification Weight Requirements

  -------------- ----------------------- --------------------------------
  Substrate      Specification           Weight Pickup Requirement
                                         (g/in^2^)

  LI-900         MC364-0006              0.4 -- 1.9

  LI-2200        MB0114-025              0.3 -- 1.8

  FRCI-12        MB0115-032              0.3 -- 1.8

  AETB-8         MB0115-049              0.4 -- 1.9

  BRI-18         MB0115-061              0.3 -- 1.8
  -------------- ----------------------- --------------------------------

NOTES: 1. In calculating the surface area for the weight pickup on tiles
with threaded inserts previously bonded to the tile, add 0.5 inch to the
radius of the hole in the base material and subtract this area from the
tile IML area.

2.  In calculating the surface area for weight pickup of tiles with
    holes, use only the IML planform area.

3.  When densifying holes only, weight pickup verification is not
    required.

**6.5 WATERPROOFING**

Densified tiles shall be waterproofed. Tiles shall be dry prior to
waterproofing.

**6.6 BOND STRENGTH**

Densification of the tile bonding surface shall result in a bonded
tile/SIP/structural strength at the tile interface to produce a minimum
stress at a failure according to Table II.

Table II. Interface Strength Requirements

  ----------------------------------- -----------------------------------
  Material                            Strength (psi)

  LI-900                              13

  LI-2200                             35

  FRCI-12                             50

  AETB-8                              29

  BRI-18                              57
  ----------------------------------- -----------------------------------

**7.0 [PROCESS VERIFICATION]{.underline}**

**7.1 LEVEL 1 PROCESS VERIFICATION**

Detailed procedures for Level 1 processing shall contain Mandatory
Inspection Points (MIP's). These MIP's shall describe or refer to
specific inspection methods and criteria with which to verify the
quality of the composite part. MIP's shall, at a minimum verify:

**7.2 LEVEL 2 PROCESS VERIFICATION**

Level 2 is classified as a non-flight article. There are no special
process verification requirements for Level 2 processing. Therefore,
MIP's are not required.

**7.3 VERIFICATION RECORDS**

Traceable records for all MIP's shall be kept as quality assurance
records.

**7.4 PRODUCT ACCEPTANCE**

Product acceptance shall be based upon evidence of compliance with the
requirements of 5.1, 6.1, 6.2, 6.3, 6.4, and 6.5.

**8.0 [TRAINING AND CERTIFICATION OF PERSONNEL]{.underline}**

Training of technicians shall be performed according to written detailed
procedures. Proper training shall, at a minimum, be structured in such a
way as to ensure that each trainee is capable of densifying tiles that
pass Level 1 process verification criteria. Training and certification
records shall be kept.

For work performed at JSC facilities, these requirements shall be
satisfied by the training and certification of personnel per TI-9009-01.

**9.0 [DEFINITIONS]{.underline}**