I am trying to make a module to hide product types when tryng to create a new product.

I have created the files as follows:

app\etc\modules\Grando_Producttype.xml


    <?xml version="1.0"?>
    <Grando_Producttype>
            <active>true</active>
            <codePool>local</codePool>
    </Grando_Producttype>

app\code\local\Grando\Producttype\etc\config.xml

    <?xml version="1.0"?>
    <config>
        <modules>
            <Grando_Producttype>
                <version>1.0</version>
            </Grando_Producttype>
        </modules>
    	<global>
        	<models>
        		<catalog>
          			<rewrite>
          				<product_type>Grando_Producttype_Model_Product_Type</product_type>
          			</rewrite>
           		</catalog>
        	</models>
    	</global>     
    </config>

app\code\local\Grando\Producttype\Model\Product\Type.php

    <?php 
    class Grando_Producttype_Model_Product_Type extends Mage_Catalog_Model_Product_Type
    {
        static public function getOptionArray()
    {
        $options = array();
        foreach(self::getTypes() as $typeId=>$type) {
            if($typeId == 'virtual'):
                $options[$typeId] = Mage::helper('catalog')->__($type['label']);
            endif;
        }
    
        return $options;
    }
    }

This should be working good I think, but for some reason it is not loading and all products still show up and I have no idea why and can't find the reason.
I am quite new to Magento. Is there any configuration I might be missing?
I've already tryed to change my class name to `Grando_Producttype_Model_Product_Type` and no success...

Cache is not activated, 

Any help will be appreciated! Thanks